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Novel Fluorescent Technique Detects Early Stage Glaucoma

By Labmedica International staff writers
Posted on 08 May 2017
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Image: The structure of the annexin 5A protein (Photo courtesy of Wikimedia Commons).
Image: The structure of the annexin 5A protein (Photo courtesy of Wikimedia Commons).
A team of British glaucoma researchers used a novel fluorescent microscopy technique to rapidly diagnose the disease at a very early stage.

Retinal cell apoptosis occurs in many ocular neurodegenerative conditions including glaucoma - the major cause of irreversible blindness worldwide. Investigators at University College London employed a new imaging technique called DARC (detection of apoptosing retinal cells), which until now had only been demonstrated in animal models. The investigators determined if the protein annexin 5 labeled with the fluorescent dye DY-776 (ANX776) could be used safely in humans to identify retinal cell apoptosis.

Annexin A5 is a cellular protein in the annexin group, which is used as a non-quantitative probe to detect cells that have expressed phosphatidylserine (PS) on the cell surface, an event found in apoptosis as well as other forms of cell death.

In the study, eight patients with glaucomatous neurodegeneration and evidence of progressive disease, and eight healthy subjects were randomly assigned to intravenous ANX776 doses of 0.1, 0.2, 0.4, and 0.5 milligrams in an open-label, phase I clinical trial. In addition to assessing the safety, tolerability, and pharmacokinetics of ANX776, the study aimed to explore whether DARC could successfully visualize individual retinal cell apoptosis in vivo in humans, with the DARC count defined as the total number of unique ANX776-labelled spots.

The results demonstrated that retinal cell apoptosis could be identified in the human retina with increased levels of activity in glaucomatous neurodegenerative disease. DARC enabled retinal cell apoptosis to be identified in the human retina using ANX776. Single annexin-labelled cells were visualized in a dose-dependent pattern up to six hours after injection. The DARC count was significantly higher in glaucoma patients compared to healthy controls, and was significantly greater in patients who later showed increasing rates of disease progression, based on optic disc, retinal nerve fiber layer, or visual field parameters. Additionally, the DARC count significantly correlated with decreased central corneal thickness and increased cup-disc ratios in glaucoma patients and with increased age.

ANX776 was found to be safe and well tolerated with no serious adverse events, and a short half-life (10 to 36 minutes).

First author Dr. Francesca Cordeiro, professor of retinal neurodegeneration and glaucoma studies at University College London, said, "Detecting glaucoma early is vital as symptoms are not always obvious. Although detection has been improving, most patients have lost a third of vision by the time they are diagnosed. Now, for the first time, we have been able to show individual cell death and detect the earliest signs of glaucoma. While we cannot cure the disease, our test means treatment can start before symptoms begin. In the future, the test could also be used to diagnose other neurodegenerative diseases."

The DARC study was published in the April 26, 2017, online edition of the journal BRAIN.

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